One way to increase engine efficiency is to reduce engine displacement and boost the engine. By boosting the engine, the engine air capacity can be increased such that additional fuel may be supplied to the engine to increase engine power output. However, it may be possible for a turbocharger waste-gate to degrade in performance during engine operation. For example, a waste-gate range of motion may be reduced during some operating conditions. If the waste-gate does not open as far as is desired, it may be difficult to control turbocharger compressor surge under some engine operating conditions. Further, the turbocharger may produce more boost than is desired during some engine operating conditions when the waste-gate range of motion is less than desired.
The inventors herein have recognized the above-mentioned disadvantages and have developed an engine method, comprising: in response to turbocharger waste-gate degradation, increasing a level of exhaust heat extracted from exhaust gas upstream of a turbocharger turbine to reduce flow through a turbocharger compressor.
By adjusting the position of a heat recovery valve in an exhaust system, it may be possible to control engine boosting and turbocharger compressor surge when a turbocharger waste-gate range of operation is degraded. In one example, if a turbocharger waste-gate is stuck in a closed position, a heat recovery valve position is adjusted such that a portion of exhaust gas energy bypasses a turbocharger turbine. Alternatively, if the turbocharger waste-gate opening amount is restricted to less than its full range of authority, the heat recovery valve can be opened in response to a condition where the waste-gate opening becomes limited. For example, if a turbocharger waste-gate freely opens to 25% if its full opening range, but if the waste-gate fails to open beyond 30% if its full opening range, the heat recovery valve may be opened further when the waste-gate position is commanded to a position that is greater than 30% of the waste-gate opening range. In this way, it is possible for an exhaust heat recovery valve to assist in controlling turbocharger boost and surge when operation of a turbocharger waste-gate becomes degraded.
The present description may provide several advantages. In particular, the approach provides an alternative or additional way to control engine boost and turbocharger compressor surge. In addition, the engine system may not have to reduce engine output as much as when a heat recovery valve is not available to control boost and compressor surge. Further still, in some examples, the heat recovery valve may be used to control turbocharger operation when the waste-gate is operating as desired but where the waste-gate position is not adjustable due to a low level of boost or due to a low level of actuation force (e.g., low vacuum pressure).
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.